The diffusion of impurities in single crystal semiconductors has been studied thoroughly. The diffusion behavior is well understood and important commercial processes, notably in silicon, are based on this understanding.
Recently, considerable experimentation by many investigators has established that short pulses of laser or electron beam radiation can be used to heal radiation damage to semiconductor crystals that occurs during implantation of impurities. See, e.g., G. A. Kachurin and E. V. Nidaev, Sov. Phys, Semiconductors 11, 350 (1977); G. Foli, E. Rimini, M Bertolotti and G. Vitali, Proc. Thin Film Symposium, Atlanta, Georgia, October 1977. (Published by the Electrochemical Society of America, J. E. Baglin and J. M. Poate, ed.); W. L. Brown et al, Proc. Conf. on Rapid Solidification Processing, Reston, VA, November 1977 (Published by the Defense Research Projects Agency and the National Bureau of Standards). In many of those experiments it was found that the boundary of the impurity region moves substantially during the annealing process. The reason for this was not known, since the movement could not be accounted for by solid state diffusion in the short treatment periods involved. Speculation followed, which we have now confirmed, that suitable pulses actually melt the regions of the semiconductor on which they are incident and those regions regrow epitaxially. The diffusion of impurities in the molten phase is substantially faster than the solid state rate--fast enough to explain the movement of the boundary.
It is evident then at this point that laser or electron beam annealing is a new processing tool, not only for annealing ion damage effectively in very short time periods, but for relocating impurities in semiconductors on a selective basis. We have devised, in addition, a technique for precisely controlling the annealing process.